Nickel plating by chemical reduction



2,774,688 7 NI KEL PLAIING BY CHEMICAL REDUC'IIGN Robert l Girard, (3hicopee -Falls, Mass.

No Drawing. ApplicationJune-d,1954,

Serial No. 433,824 I '2 Claims. *(61. 117-430) This invention relates to nickel plating by chemical reduction.

United States P Plating ;.proce dur e s have been aknjown which *hau'e 1 the objections that a dull and rough coating is deposited that is not suitable for many purposes.

According to this invention, it has been discovered that when boric acid and ammonium chloride are added to an autocatalystic chemical reduction process, that the physical properties of the nickel deposit is improved. That is, a very bright and smooth nickel deposit is accomplished which is characterized by its hardness and adherent properties while at the same time it has a very low or practically no stress.

Accordingly, a bath including the following constituents within the ranges specified has been found to give good results in connection with 72 sq. inches of surface per one gallon of bath or solution:

Nickel sulfate, 5 to 100 grams/l.

Sodium hypophosphite, 10 to 80 grams/l. Sodium acetate, 1 to 20 grams/l.

Boric acid, 1 to 60 grams/l.

Ammonium chloride, 0 to 40 grams/l.

However, very desirable results were obtained with the following bath where the constituents were approximately as stated:

Nickel sulfate, 80 grams/l.

Sodium hypophosphi-te, 24 grams/l. Sodium acetate, 12 grams/l.

Boric acid, 8 grams/l.

Ammonium chloride, 6 grams/l.

A bath of the foregoing constituents has been used within the temperature range 180 F. to 210 F. but the preferred temperature range is from 196 to 204 F.

The optimum pH is from 4.6 to 5.0 and for best results should be maintained after, say an hours operation by the addition of a small amount of sodium hydroxide. Dullness and roughness of plate will result from a pH above 6.0 or below 4.0 and is to be avoided.

Plating rates for 72 square inches of surface have been found to vary somewhat according to temperature of the bath as follows:

A. 180 .to 190 F., .0005 to .0006 inch. B. 190 to 195 F., .0006 to .0007 inch. C. 196 to 204 F., .0007 to .00085 inch. D. 205 to 210 F., .00085 to .0011 inch.

As will be seen at the preferred temperature, there is a very desirable deposit whereas with higher temperature the coating is not as smooth.

A very smooth and bright deposit of .0005 of an inch 2,774,688 Patented Dec. 18, 1956 ":2 has indicated -=good corrosion resistance and fine amorphous structureduring 200-hours inasaltspray.

This boric acid can be added invarious amounts which range-from-%"to-4 ozaper gal. without altering the rate of plate too greatly. .It has been found that the best bright and' more ductile deposits occur with an addition of 102. per gel. to the bath, but a bright deposit will occur as the amount of boric acid ai-sincrease'd. 'Then tests have shown that the brighter the deposit the more brittle the plated coating is. Therefore, tests have shown, that a maximum -of =1% oz. per gal. is the mostthat-can-be added to this'bath and still get a fairly ductileplate.

'The properconcentr'ation of 'boricacid' not only controls the nickel ions in the solution so as to deposit *a smooth plate, but also wi-ll'brig hten upthe plated coating,thus depositing asmooth, bright deposit. Though the hardness 'of'tlr'is-plateis comparable to that of'electrol'ytic hard *nickel' i-t was-found that the deposits given offin the reaction were quite easily-bu'ifed to a very high =luster.

Ammonium chloride is employed in this particular "bath fbecause-we -have beenstriving for a low stress Electroless NickelSolu-tion.

Prior to this invention ammonium chloride has been used in an alkaline bath containing nickel sulfate, but its concentration was such that it gave off a very undesirable odor, and .too high a concentration tends to reduce the rate of the reaction.

This invention uses ammonium chloride to obtain a low stress nickel bath and should be good for electrotyping where it has been proven that a nickel sulfate bath containing a small amount of ammonium salt will give satisfactory adhesion to even a graphite mold. This is a very severe test of a good adherent nickel deposit.

In testing panels of 1045 steel it was noted that a bend test at on a nickel coated panel, without ammonium chloride in the bath flaked on the internal part of the bent panel. When ammonium chloride was added to the bath and the same bend test applied to the work, flaking was practically eliminated, if not eliminated altogether. The coating was also quite adherent and a file was run across the bent surface and it appeared to have little effect in loosening the nickel deposit.

-On heavy deposits of nickel such as .0035 on a side, it was noted that the adhesion of the plate from a bath containing boric acid and ammonium chloride, both in the amount recommended, deposited a more adherent coating with lower stress and a brighter and smoother deposit, than a bath containing neither of the above mentioned addition agents.

In a bend test of 180 a panel containing a deposit of .0035 on the side showed that the nickel deposit, even when stretched almost apart completely would adhere very well to the base of the 1045 steel panel.

A solution was made up having boric acid and ammonium chloride in the amount of 8 and 6 grams/l. respectively. The temperature was 200 F. and a pH of 4.8 to 5.8 was maintained during the one hour of operation. The deposit was smooth, bright and adherent and a rate of .00085 per hour was maintained.

More tests have been conducted with the particular solution and the bath has been operated as long as 8 hours continuously resulting in an average deposit of .0006 per hour on the side and a bright, smooth and adherent coating has been obtained.

Therefore, boric acid as an agent used in controlling the chemical reaction of the nickel sulfate electroless nickel bath shows that the reaction that takes place is such that it changes the physical properties of the deposit from the previously known nickel sulfate bath making them more desirable from the standpoint of a bright,

jsmooth depositand at the same time no loss in the rate of deposit is caused.

Thus, in this case boric acid is not acting exclusively as .a bufier, as the rate of plate is not slowed down, as would be the case if boric acid were buffering the bath. Instead boric acid seems to suspend the nickel ion in the bath in such a manner that a smooth, bright adherent deposit is achieved without affecting the rate of plate.

In general the process is applicable to the plating of nickel on a large group of metals such as steel, iron platinum, silver, gold, copper, aluminum, cobalt, palladium, brass, bronze, and titanium.

Having thus described the invention and the best method of practicing the new process for forming this novel composition, without being limited to the order of steps of such process as herein recited, or to the proportions of parts employed therein, or to the precise ingredients named therein, as it is evident that each of these ingredients has a considerable range of equivalents, and as it is also evident that the order and proportions of the process may be carried out without departing from its scope and purposes, what it is desired to claim and secure by Letters Patent of the United States is:

l. A bath for nickel plating by chemical reduction with a controlled nickel sulphate solution comprising, nickel s pha e ou s am L o m hypophosphite bou 24 grams/1., sodium acetate about 12 grams/1., boric acid about 8 grams/ 1., and ammonium chloride about 6 grams/l.

2. A method fior nickel plating by chemical reduction comprising the step of immersing a metal article from the group consisting of iron, platinum, silver, gold, copper, palladium, brass, bronze and titanium into a controlled nickel sulphate solution including the following constituents in the following amounts per litre, nickel sulphate about grams/1., sodium hypophosphite about 24 grams/1., sodium acetate about 12 grams/1., boric acid about 8 grams/1., and ammonium chloride about 6 grams/ 1., at a temperature of between 196 F. and 204 F.

References Cited in the file of this patent UNITED STATES PATENTS 2,265,467 Alexander et a1 D65. 9, 1941 2,461,933 Smith et a1. Feb. 15, 1949 2,532,283 Brenner Dec. 5, 1950 2,539,247 Hensel Jan. 23, 1951 2,646,456 Jacquier July 21, 1953 FOREIGN PATENTS 562,046 Great Britain June 15, 1944 

2. A METHOD FOR NICKEL PLATING BY CHEMICAL REDUCTION COMPRISING TH STEP OF IMMERSING A METAL ARTICLE FROM THE GROUP CONSISTING OF IRON, PLATINUM, SILVER, GOLD, COPPER, PALLADIUM, BRASS, BRONZE AND TITANIUM INTO A CONTROLLED NICKEL SULPHATE SOLUTION INCLUDING THE FOLLOWING CONSTITUENTS IN THE FOLLOWING AMOUNTS PER LITRE, NICKEL SULPHATE ABOUT 80 GRAMS/1., SODIUM HYPOPHOSPHITE ABOUT 24 GRAMS/1., SODIUM ACETATE ABOUT 12GRAMS/1., BORIC ACID ABOUT 8 GRAMS/1., AND AMMONIUM CHLORIDE ABOUT 6 GRAMS/ 1., AT A TEMPERATURE OF BETWEEN 196* F. AND 204 * F. 